Vehicle guidance systems

ABSTRACT

A vehicle guidance system in which a vehicle (e.g., a tractor) follows a conductor carrying a guidance signal. Steering control is effected in response to an error signal representative of divergence of the vehicle from the required track. A pulse generator gives a variable mark/space ratio output in accordance with the amplitude of the error signal and the pulse generator output is directed to operate a left- or right-hand on-off fluid valve in accordance with the sign of the error signal. The fluid valves are thus controlled by the variable mark/space signal to give proportional control although they are on-off valves.

United States Patent Hobday et al. July 25, 1972 [54] VEHICLE GUIDANCESYSTEMS 3,513,931 5/1970 Warner et a1. ..l80/98 Inventors: StephenWilliam y; David Stephen M05811}: ..3l8/576 Hobday both of 219 SycamoreRd Farm Zwory 1n et ..|80/98 g England 2,921,179 1/1960 Anderson..3l8/576 [22] Filed: June 29, 1970 Primary Examiner-Kenneth H, Betts A"-W d th,Ll d&P k 211 App]. No.: 50,398 m mm [57] ABSTRACT [30] I ForeignApplication Priority A vehicle guidance system in which a vehicle (e.g.,a tractor) July 1, 1969 Great Britain ..33 286/69 a carrying a guidanceSignal Steering trol is effected in response to an error signalrepresentative of 52 us. 01. ..1s0/9s, 180/792 R divergence the which?fmm required rack A Pulse [51] lnt.Cl ..B62d1/24 generator gives avariable mark/space ratio output in ac- [58] Field of Search ..180/98 7979.1 82- 172/2 amplitude Signal and the Pulse 172/6. 318/576 6 generatoroutput is directed to operate a leftor right-hand on-off fluid valve inaccordance with the sign of the error [56] References Cited signal. Thefluid valves are thus controlled by the variable mark/space signal togive proportional control although they U NlTED STATES PATENTS r nffvalves.

3,482,644 12/1969 Krieger et a1. 180/98 5 Claims, 3 Drawing figuresPatented July 25, 1972 3,679,019

2 Sheets-Sheet 1 STEPHEN WILLIAM HOBDAY and DAVID STEPHEN HOBDAY,Inventors BY 14 44014 ,ZA/M

Attorneys Patented July 25, 1972 2 Sheets-Sheet 2 STEPHEN WILLIAM HOBDAYand R MW DAVID STEPHEN HOBDAY, Inventors dtullllfllfflM/M AttorneysVEHICLE GUIDANCE SYSTEMS This invention relates to vehicle guidancesystems of the kind in which the movement of the vehicle is controlledby signals emitted from a conductor arranged along the path on which thevehicle is to travel.

In such systems the vehicle carries a device which responds to signalsin the conductor to produce an error signal which varies in magnitudeand sign according to the divergence of the actual path of the vehiclefrom the path it is required to follow. Such error signal is applied tocontrol the supply of pressure fluid to either end of a cylinder thepiston in which is connected with the steering gear of the vehicle. Inknown systems this has required the use of expensive and complicatedarrangements of control valves and it is an object of the presentinvention to provide an improved arrangement which is cheaper tomanufacture and simpler in use.

According to the present invention there is provided a vehicle guidancesystem in which a vehicle is steered to follow a conductor in responseto signals emitted by the conductor, the vehicle having mounted thereona signal detector; discriminator means for deriving from the signaldetector an error signal representative of the steering error inmagnitude and sign; a pulse-train generator for generating a train ofcontrol pulses having a mark/space ratio dependent upon the magnitude ofthe error signal; gate means for directing the pulse train to energize afirst or a second steering solenoid in dependence on the sign of theerror signal; and a fluid-actuated steering ram arrangement providedwith right and left on-off valves operated respectively by the first andsecond solenoids to steer the vehicle to the right and left.

By using solenoid operated on-off valves of conventional type,considerable economies can be effected and it has also been found thatwhen modulated by the pulse generator in the manner described thequantity of fluid passed in a given time varies substantially linearlywith variations in magnitude of the error signal.

Preferably the signal detector comprises a pair of mutuallyperpendicular coils and the discriminator means comprises a phasediscriminator which derives a signal representative of the phasedifference of the signals in the two coils. Preferably the coils arevertical and horizontal, in which case the horizontal coil may beregarded as the reference coil and the vertical coil as the detectorcoil.

Preferably there is included a feedback circuit mechanically coupled tothe vehicle steering mechanism to generate a feedback signal which iscombined with the output from the discriminator means to give the errorsignal.

The invention will further be described with reference to theaccompanying drawings, of which:

FIG. 1 is a diagrammatic elevation of a tractor being guided by a systemin accordance with the invention;

FIG. 2 is an electrical circuit diagram of the guidance apparatuscarried by the tractor of FIG. 1; and

FIG. 3 is a hydraulic circuit diagram of the steering mechanism for thetractor.

Referring to FIG. I, there is shown a tractor I automatically ploughinga field beneath the surface 2 of which have been buried an insulatedguide conductor wire 3 having a number of parallel runs along the field.The wires are about 6 meters apart and one-half meter deep. They carry acontinuous tone currentof 2 kHz and the consequent alternating field isdetected by a detector head 4 carried on the tractor. Head 4 is carriedon a boom 5 across the front of the tractor and is movable along theboom so that the tractor may follow the same conductor wire for severalparallel runs across the field, with appropriate shifting of the head 4.

The detector 'head has a vertical pick-up coil 6 and a horizontalpick-up coil 7 wound on ferrite rods. With this arrangement the relativephase of the 2 kHz currents induced in the two coils changes inaccordance with the position of the detector head with respect to theguide wire. With the head directly above a guide wire there is no phasedifference. If the head is then moved to the right or left there is aphase difference in an appropriate sense and of a magnitude proportional to the distance moved.

FIG. 2 is a diagram of the steering control circuit which is mounted onthe tractor in a box 8 (FIG. 1). Referring to FIG. 2, the outputcurrents from coils 6 and 7 are fed through tuned amplifiers 9 and 10respectively and additional amplifiers II and 12 to a phasediscriminator 13 which charges one or other of capacitors l4 and 15,depending on the sense of the phase difference, with a voltage of amagnitude dependent upon the size of the phase difference. The outputfrom the discriminator is derived on a lead 16 with respect to avariable reference voltage from a potentiometer I7. Adjustment ofpotentiometer 17 is effective to vary the zero phase point of thediscriminator, so that under some circumstances zero output may be givenwhen the detector head is not directly over the wire 3.

The discriminator output is applied to a feedback amplifier 18 throughan input limiter 19 to avoid amplifier saturation. The output fromamplifier I8 is thus a unidirectional signal, the sign and amplitude ofwhich is dependent upon the sense and magnitude of the divergence of thetractor from the required path. This signal may be used directly tocontrol the steering correction. However, in order to avoid overshoot ofthe steering correction and provide control stability this signal iscombined with a feedback signal representative of the instantaneousattitude of the steering mechanism. The feedback signal is derived froma potentiometer 20 coupled to the steering mechanism. Sensitivitycontrol is effected by means of a potentiometer 21. I

The discriminator output and feedback signal are added at a summingpoint 22. The lead or lag of the feedback signal may be adjusted toalter the control characteristics by switching additional by-passcapacitors 23 for input resistor 24. Thus, if a left-hand correction isrequired and the steering wheels are already directed appropriately, thesignal from the discriminator is annulled to a large extent by thefeedback signal. The combined discriminator and feedback signal is theerror signal.

The error signal is applied to a buffer amplifier 25 and thence to anamplifier 26, the output from which is applied to one input of a bridgerectifier circuit 27. The output from amplifier 26 is also applied tothe input of a unity gain inverting amplifier 28, the output of which isapplied to the other input of the bridge rectifier circuit 27. Theoutput from circuit 27 is represented by the difference in voltageacross capacitors 29 and 30, and is dependent only on the amplitude ofthe error signal and not upon its sign.

The voltages on capacitors 29 and 30 are applied respectively to thebases of a pair of transistors 31, 32 which are coupled as afree-running multi-vibrator giving a square wave pulse train at itsoutput 33 of 10 Hz. The mark/space ratio of this output is variable anddepends upon the amplitude of the voltage difference across bridge 27.The pulse generator circuit is adjusted so that at the minimum, when theerror signal amplitude is lowest, the mark time of its output is 10percent. When the error signal amplitude is maximum the mark time ispercent.

The output at 33 is amplified by transistors 34, 35 and appliedseparately to the inputs of two inverters 36, 37. However, only oneinverter at a time actually receives an input because of control by agating circuit 38. In the gating circuit one or other of transistors 39,40, conducts at any one time in accordance with whether the sign of theerror signal is positive or negative, requiring a left or right-handsteering correction. The sign of the error signal is determined by zenerdiodes 41, one of which receives an error signal input directly from theoutput of an amplifier 42 connected to the output of buffer amplifier25. The other zener diode receives an input from a unity gain invertingamplifier 43 which processes the signal from amplifier 42. Thus, thepulse train signal to one of the invertors 36, 37 is short circuited bythe appropriate transistor 39, 40 when the error signal sign indicatesthat it is the other steering channel which should be operative.

lnvertor 36 controls the left turn steering channel and applies thecontrolling pulse train through amplifiers to a sole noid 44 which opensa valve in response to the marks" to turn the tractor left. inverter 37similarly operates a right turn solenoid 45. In order to ensure thatonly one steering channel operates at a time there is provided aninterlock arrangement 46 comprising diodes and invertors 47 so arrangedthat pulse train signals applied in one channel are effective to inhibitthe other channel from operating.

Referring now to H6. 3, there is shown the hydraulic circuit for thetractor. The steering control rod (not shown) of the tractor is fixed tothe rod 48 of a double-acting hydraulic ram 49. Fluid is admitted to oneside or the other of the ram piston 50 by on-off valves 51, 52 which areoperated by the solenoids 44, 45 respectively. The valves arespring-return valves and they are opened by the marks" of the pulsetrain, at a frequency of l Hz. The hydraulic reservoir 53, pump 54 andpressure control valve 55 are shown.

It will be seen that the control of the mark" time down only to percentallows the oscillator to run continuously and errors due to stopping andre-starting the oscillator are avoided.

The setting of the potentiometers at the inputs of amplifiers 42 and 43control the points at which the zener diodes 41 start to conduct. Inpractice these potentiometers are set so that there is a region aboutthe central position in which both zener diodes conduct simultaneously,so that no output signal is given in either control channel. This givesa dead space in the control characteristics at the central position ofthe tractor. This alleviates any tendency of the steering control tohunt.

We claim:

1. A vehicle guidance system in which a vehicle is steered to follow anelectric conductor in response to signals emitted by the conductor, thevehicle having mounted thereon a signal detector comprising a pair ofmutually perpendicular coils; a phase discriminator for deriving fromthe phase difference of signals in the two coils, an error signalrepresentative in magnitude and sign of the positional error of thevehicle in relation to the conductor; a pulse-train generator forgenerating a train of control pulses having a mark/space rationdependant upon the magnitude of the error signal; gate means fordirecting the pulse train to energize a first or a second steeringsolenoid in dependence on the sign of the error signal; and afluid-actuated steering ram arrangement provided with right and leftonoff valves operated respectively by the first and second solenoids tosteer the vehicle to the right and left.

2. A system as claimed in claim 1, wherein one coil has a vertical axisand the other coil has a horizontal axis.

3. A system as claimed in claim 1, including a feedback circuitmechanically coupled to the vehicle steering mechanism to generate afeedback signal which is combined with the output from the discriminatormeans to give the error signal.

4. A system as claimed in claim 1, wherein the steering solenoids opentheir respective on-off valves when receiving the marks of the pulsetrain and the pulse-train generator has a range of mark time controlfrom 10 to percent.

5. A system as claimed in claim 1, wherein the frequency of the pulsetrain is approximately 10 Hz.

1. A vehicle guidance system in which a vehicle is steered to follow anelectric conductor in response to signals emitted by the conductor, thevehicle having mounted thereon a signal detector comprising a pair ofmutually perpendicular coils; a phase discriminator for deriving fromthe phase difference of signals in the two coils, an error signalrepresentative in magnitude and sign of the positional error of thevehicle in relation to the conductor; a pUlse-train generator forgenerating a train of control pulses having a mark/space rationdependant upon the magnitude of the error signal; gate means fordirecting the pulse train to energize a first or a second steeringsolenoid in dependence on the sign of the error signal; and afluidactuated steering ram arrangement provided with right and lefton-off valves operated respectively by the first and second solenoids tosteer the vehicle to the right and left.
 2. A system as claimed in claim1, wherein one coil has a vertical axis and the other coil has ahorizontal axis.
 3. A system as claimed in claim 1, including a feedbackcircuit mechanically coupled to the vehicle steering mechanism togenerate a feedback signal which is combined with the output from thediscriminator means to give the error signal.
 4. A system as claimed inclaim 1, wherein the steering solenoids open their respective on-offvalves when receiving the ''''marks'''' of the pulse train and thepulse-train generator has a range of ''''mark'''' time control from 10to 100 percent.
 5. A system as claimed in claim 1, wherein the frequencyof the pulse train is approximately 10 Hz.